The present invention relates to a heat-sealing sheet material which can be used, for example, as a material for covers to be affixed onto the opening rims of glass containers for food products.
As examples of the adhesive resins for glass, there are known formal resins, polyvinyl formal, ethylene/vinyl acetate copolymers and partially-saponified products of ethylene/vinyl acetate copolymers. These adhesive resins are being used mainly as an intermediate bonding layer of laminated glasses or a coat on glass containers for breakage prevention.
As the heat-sealing sheet materials for glass containers, there are known hot-melt processed sheet materials in which an ethylene/vinyl acetate copolymer having a high vinyl acetate content or a partially-saponified product of an ethylene/vinyl acetate copolymer is mixed with additives such as tackifier and wax. Because of their deficient water resistance, these materials are used only for glass containers for powdery food products and cannot be applied for the containers for foods of high water content such as jams and pickles.
Of the above heat-sealing sheet materials, those containing aldehydes such as formal resins and polyvinyl formal have high water resistance. However, their use in food packaging is not desirable because of toxicity from the standpoint of food sanitation.